Zeolite molecular sieves are widely used in the catalyst field due to their homogeneous and ordered micropores, great specific surface and high hydrothermal stability. Zeolites in small crystal size have short intragranular diffusion pore channels and great external surface, which are advantageous to increasing the opportunities of contacting the reactants with the active sites in micropores, so as to improve the properties of zeolites. Said zeolites show their unique advantages in the reaction, such as particular macromolecular selectivity, relatively higher catalytic activity, longer catalytic lifetime and the like. However, the size of zeolites is too small to be convenient in the practical application. Moreover, such zeolites are difficult to be recovered, easily inactivate and aggregate. The addition of the binder is necessary in the shaping process, which results in the reduction of effective surface areas and introduces the diffusional limitation. Binder-free zeolite molecular sieves are zeolite particles containing no inert binders or a small amount of inert binders and having a higher zeolite content. Therefore, they may have much effective surface area and better catalytic property.
Diatomite is an aluminosilicate-enriched mineral substance. Anderson disclosed that, by secondary growth method, diatomite supported in the zeolite seed crystal grew by the action of the external silica source and alumina source, and thereby a zeolite film was formed on the surface of diatomite [S. M. Holmes et al. Stud. Surf. Sci. Catal., 2001, 135, 296.]. On the premise of retaining the characteristic multilevel-pore structure of diatomite, Wang carried out the crystal transition of diatomite to the zeolite materials having a multilevel-pore structure [Y. J. Wang et al. J. Mater. Chem., 2002, 12, 1812.].
Due to peculiar pore channel structure and better catalytic property, ZSM-5 molecular sieve becomes a very important shape selective catalytic material, and is widely applied in the organically catalytic conversion The binder conversion process is one of those for the preparation of binder-free zeolite molecular sieves. Long Yincai discloses the preparation of a binder-free ZSM-5 type hydrophobic silicon zeolite by mixing a ZSM-5 type hydrophobic silicon zeolite powder with a binder containing silicon oxide, shaping the mixture and drying, and then crystallizing and calcining the mixture in an organic amine or quaternary ammonium aqueous solution, or in a vapor [Long. Y C, Binder-Free Hydrophobic Silicon Zeolite Adsorbent and Preparation thereof, Patent No:ZL 94112035.X]. U.S. Pat. Nos. 5,665,325 and 6,458,736 disclose a process for producing binder-free MFI zeolites, and the use thereof in the hydrocarbon catalytic reaction. Said process comprises preparing MFI zeolite powder first and shaping with an amorphous silicon oxide, and converting the shaped product to MFI in small crystal size by hydrothermal crystallization, wherein zeolite phases newly formed grew around the initial zeolite molecular sieves in large crystal size, and were interwoven together. In said process, the initial powder of zeolites needs to be prepared first, mixed with the binder for shaping, and then subject to the crystallization treatment. Diatomite, carbon white or mixtures thereof as the primary materials are kneaded together with the seed crystal orienting agent and a suitable amount of silica sol or water glass, and shaped. Then, the shaped product is converted to integrative ZSM-5 binder-free shaped zeolite in small crystal size. By this process, the silica and alumina materials may be conveniently and simply converted to ZSM-5 binder-free shaped zeolite in small crystal size. The process of the present invention may be developed into an economical process for producing zeolite molecular sieve catalytic materials. Moreover, integrative ZSM-5 binder-free shaped zeolite in small crystal size has more macroporous structures, and can have synergistic effects in the practical catalytic reaction with micropores in the zeolite crystals. For example, micropores are used as the reaction place, and macropores are used as the transportation channel of the reactant molecules, so as to eliminate the diffusional limitation and effectively utilize zeolites.